There is a wide variety of diuretic-induced metabolic abnormalities of unequal severity. Renal failure can be caused by excessive sodium loss, or by certain drug combinations comprising, for instance, a nonsteroidal anti-inflammatory drug (NSAID) or an ACE inhibitor. Hyponatraemia is uncommon. It is encountered with thiazides, especially among women. A sodium level less than 120 mmol/L may result in neurological complications. Hypokalaemia is frequent and might increase the risk of cardiac arrhythmia. Hyperkalaemia induced by potassium-sparing diuretics is often combined with another contributive cause. Glucidic, lipidic and uric acid abnormalities are common, but their clinical effects are slight. They do not seem to worsen cardiovascular risks among elderly patients. Nevertheless, prescribing diuretics for elderly patients requires special precautions. Reducing the diuretic dose, as is now recommended for treating hypertension, seems to lessen adverse effects, and despite all the adverse reactions just mentioned, it has been proven that diuretics are beneficial in many diseases.